1. Field of the Invention
The present invention relates to a digital fluorographic method and system, and, more particularly, to a method and system which calls for the digitization and storage of first and second x-ray picture data derived prior to and after, respectively, injection of a contrast medium into a subject. The method and system of the invention utilize various techniques, and combinations of techniques, to develop a pictorial representation of the differences between the x-ray picture prior to injection of the contrast medium and the x-ray picture after injection of the contrast medium.
2. Description of the Prior Art
Many of the most important potential applications of computer picture processing, particularly in the field of clinical x-rays and fluorography, have not yet been successfully carried out on a feasible basis because of one fundamental difficulty. Applications, such as the analysis of fluoroscopic images, require an evaluation of the "texture" of an object before and after the injection of a contrast medium. Some work has been done in this area in an effort to improve real-time digital x-ray imaging. Typical of such efforts are the following U.S. Pat. Nos. 3,854,049; 3,894,181; 3,974,386; 4,204,225; and 4,204,226.
Considering U.S. Pat. No. 4,204,225, that patent discloses a real-time digital x-ray subtraction imaging method and apparatus having application in conducting diagnostic x-ray studies of humans and animals, and, in particular, in visualizing the cardiovascular system, including the heart and blood vessels which are of interest. Other applications for such imaging methods and apparatus include visualizing the motion of the heart in real time, displaying the circulation of the blood in the arteries and veins associated with the heart, and conducting x-ray studies of the abdomen and brain.
Such prior art techniques have been directed to achievement of improved television difference images, in which the blood vessels (for example) are shown with greatly enhanced visibility, while image elements due to bone and soft tissue are largely eliminated. Such methods and apparatus typically employ subtraction techniques for accomplishing this purpose. As a result of such subtraction techniques, television difference images are produced. In such television difference images, the visibility of an x-ray contrast medium (injected into the subject) is enhanced.
Despite such techniques of the prior art, however, the quality of the resulting x-ray images is still in need of substantial improvement. This is a result of the fact that techniques of the prior art, such as disclosed in the prior patents mentioned above, have merely employed relatively simplistic known techniques, such as enhancement, integration and subtraction. For example, U.S. Pat. No. 3,854,049 merely performs simple image subtraction of two x-ray images. U.S. Pat. No. 3,894,181 merely performs two complementary subtractions of two images, and integrates the differential portions thereof while subtractively combining the nondifferential portions thereof. U.S. Pat. No. 3,974,386 utilizes a relatively simple technique of combining first, second and third x-ray images, by means of which technique the first and third images are averaged, and the resulting average is subtractively combined with the second image. Finally, U.S. Pat. Nos. 4,204,225 and 4,204,226 also utilize a relatively simplistic technique, involving the conversion of an x-ray image into a series of television fields comprising trains of analog video signals, converting the analog video signals into digital form, integrating the resulting digital signals over a series of successive time intervals, and performing a series of subtractions between each set of integrated video signals and the preceding set of integrated video signals to produce a series of successive digital difference video signals which are then converted to analog form and displayed. Prior to conversion to analog form, conventional enhancement of the digital difference video signals can, according to the latter patents, be carried out. In addition, according to U.S. Pat. No. 4,204,225, a contrast medium can be injected prior to the subtraction process and with such timing that the contrast medium appears in the x-ray image subsequent to the time interval over which the digital video signals were integrated.
As is clear from the preceding discussion, prior art practitioners have only employed such procedures as integration, enhancement and subtraction in their quest for improved subtraction or difference imaging techniques. As a result, such techniques are still lacking in quality of the difference image resulting therefrom. In addition, the prior art technology, in general, and the aforementioned patents, in particular, have not provided an integrated system for carrying out difference imaging in as highly an efficient manner as is possible, utilizing current technology, and have not provided an integrated system wherein the system operator can simultaneously view the original x-ray picture (prior to injection of the contrast medium), the subsequent x-ray picture (subsequent to injection of the contrast medium), the difference image resulting from a subtractive combination of the original and subsequent x-ray images, and an enhanced version of the resulting difference image. The provision of such an integrated system for simultaneously displaying the aforementioned images would represent a significant improvement over the prior art, and would have substantial and obvious advantages to the medical diagnostician and to the users of such a system.